Substrate improvements for thermally imageable composition and methods of preparation

ABSTRACT

The present invention includes a radiation-imageable element for lithographic printing having a hydrophilic anodized aluminum base with a surface having pores and a image-forming layer having polymer particles coated on the aluminum base. The ratio of the average pore diameter to the average particle diameter is from 0.4:1 to 10:1. The present invention further includes a method of producing the imaged element. The method includes the steps of imagewise exposing the radiation-imageable element to radiation to produce exposed and unexposed regions and contacting the imagewise exposed radiation-imageable element and a developer to remove the exposed or the unexposed regions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imageable element and a method ofproducing an imaged element that can be used in lithographic printingplates. More particularly, the present invention relates to an imageableelement comprising a hydrophilic anodized aluminum base and coatedthereon an image-forming layer comprising polymer particles and a methodof producing the same.

2. Description of the Prior Art

Lithography is the process of printing from specially prepared surfaces,some areas of which are capable of accepting lithographic ink, whereasother areas, when moistened with water, will not accept the ink. In theart of photolithography, a photographic material is made imagewisereceptive to oily inks in the photo-exposed (negative-working) or in thenon-exposed areas (positive-working) on a hydrophilic background. Theareas which accept ink form the printing image areas and theink-rejecting areas form the background areas.

In the production of common lithographic printing plates, also calledsurface litho plates or planographic printing plates, a support that hasaffinity to water or obtains such affinity by chemical treatment iscoated with a thin layer of a photosensitive composition. Coatings forthat purpose include light-sensitive polymer layers containing diazocompounds, dichromate-sensitized hydrophilic colloids and a largevariety of synthetic photopolymers, particularly diazo-sensitizedsystems, which are widely used. Upon image-wise exposure of thelight-sensitive layer the exposed image areas become insoluble and theunexposed areas remain soluble. The plate is then developed with asuitable liquid to remove the diazonium salt or diazo resin in theunexposed areas.

Eurpean Patent Application No. 849,091 A1 and U.S. Pat. No. 6,001,536disclose thermal coalescence of imageable compositions, includingon-press developable compositions. These patent do not contain anydisclosure regarding the oxide pore size on the surface of the substrateor the relationship of the oxide pore size to the particle size of thepolymer in the image-forming layer.

U.S. Pat. No. 4,990,428 discloses an aluminum substrate having an oxidelayer with 35-100 nm pore diameters, obtained by using phosphoric acidas the main electrolyte in the anodization process. When this substrateis overcoated with a free radical photo-polymerizable compositioncontaining carboxylic acid groups and cured, the resulting lithographicplate exhibits superior press life. As above, this patent also does notcontain any disclosure regarding the relationship of pore size toparticle size of the polymer in the image-forming layer.

U.S. Pat. No. 4,865,951 discloses a bilayer anodic surface produced in a2-stage process, which affords average pore size diameters of 10-75 nmin the upper layer and substantially greater diameters in the lowerlayer. A lithographic printing plate comprising an imageable layer onthis support is shown to improve stain resistance. However, there is nodisclosure regarding the relationship of pore size to particle size.

U.S. Pat. No. 5,922,507 discloses a photosensitive imaging elementhaving a two-phase layer on a support. The two-phase layer has ahydrophilic continuous phase containing a hardened hydrophilic polymerand a dispersed hydrophobic photopolymerizable phase that has amultifunctionally polymerizable monomer and a photoinitiator. Thehydrophobic photopolymerizable phase is formed of particles having anaverage particle size comprised between 0.1 and 10 μm, i.e., 100-10,000nm. Neither pore size on the support nor pore size/imaging layerparticle size matching are mentioned.

The present invention provides average pore diameter to average particlediameter ratios that can enhance adhesion, which enhances thesensitivity and the press life of the printing plates preparedtherefrom.

SUMMARY OF THE INVENTION

The present invention includes a radiation-imageable element forlithographic printing. The radiation-imageable ellement comprises ahydrophilic anodized aluminum base having a surface comprising pores,and coated thereon, an image-forming layer comprising polymer particles,the ratio of said average pore diameter to said average particlediameter being from about 0.4:1 to about 10:1.

The present invention also includes a method of producing an imagedelement. The method comprises the steps of:

providing a radiation-imageable element for lithographic printingcomprising: a hydrophilic anodized aluminum base having a surfacecomprising pores; and coated thereon, an image-forming layer comprisingpolymer particles, the ratio of the average pore diameter to the averageparticle diameter being from about 0.4:1 to about 10:1; and

imagewise exposing the radiation-imageable element to radiation toproduce exposed and unexposed regions.

The present invention further includes a method of producing an imagedelement having complementary ink receiving and ink rejecting regions.The method comprises the steps of:

providing a radiation-imageable element for lithographic printingcomprising: a hydrophilic anodized aluminum base having a surfacecomprising pores; and coated thereon, an image-forming layer comprisingpolymer particles, the ratio of the average pore diameter to the averageparticle diameter being from about 0.4:1 to about 10:1;

imagewise exposing the radiation-imageable element to radiation toproduce exposed and unexposed regions; and

contacting said imagewise exposed radiation-imageable element and adeveloper to selectively remove said exposed or said unexposed regions.

The present invention provides average pore diameter to average particlediameter ratios that can enhance the interaction of the image-forminglayer with the substrate surface layer following thermal imaging byallowing the polymer particles to enter into the oxide pores of thesubstrate, thereby enhancing adhesion. The enhanced adhesion, in turn,will enhance the sensitivity and the press life of the printing plates.

DETAILED DESCRIPTION OF THE INVENTION

Lithographic printing is based on the immiscibility of oil and water.Ink receptive areas are generated on the surface of a hydrophilicsurface. When the surface is moistened with water and then ink isapplied, the hydrophilic background areas retain the water and repel theink. The ink receptive areas accept the ink and repel the water. The inkis transferred to the surface of a material upon which the image is tobe reproduced. Typically, the ink is first transferred to anintermediate blanket, which in turn transfers the ink to the surface ofthe material upon which the image is thereafter reproduced.

Lithographic printing plate precursors, i.e., imageable elements,typically include an imageable coating applied over the hydrophilicsurface of a support material. If after exposure to radiation, theexposed regions of the coating become the ink-receptive image regions,the plate is called a negative-working printing plate. Conversely, ifthe unexposed regions of the coating become the ink-receptive imageregions, the plate is called a positive-working plate. In the presentinvention, the imagewise exposed regions are rendered less soluble ordispersible in a developer and become the ink-receptive image areas. Theunexposed regions, being more readily soluble or dispersible in thedeveloper, are removed in the development process, thereby revealing ahydriphilic surface, which readily accepts water and becomes theink-repellant image area.

The term “graft” polymer or copolymer in the context of the presentinvention refers to a polymer which has as a side chain a group having amolecular weight of at least 200. Such graft copolymers can be obtained,for example, by anionic, cationic, non-ionic, or free radical graftingmethods, or they can be obtained by polymerizing or co-polymerizingmonomers, which contain such groups.

The term “polymer” in the context of the present invention refers tohigh and low molecular weight polymers, including oligomers, andincludes homopolymers and copolymers. The term “copolymer” refers topolymers that are derived from two or more different monomers.

The term “backbone” in the context of the present invention refers tothe chain of atoms in a polymer to which a plurality of pendant groupsare attached. An example of such a backbone is an “all carbon” backboneobtained from the polymerization of an olefinically unsaturated monomer.

The term “hydrocarbyl” in the context of the present invention refers toa linear, branched or cyclic alkyl, alkenyl, aryl, aralkyl or alkaryl of1 to 120 carbon atoms, and substituted derivatives thereof. Thesubstituent group can be halogen, hydroxy, hydrocarbyloxy, carboxyl,ester, ketone, cyano, amino, amido and nitro groups. Hydrocarbyl groupsin which the carbon chain is interrupted by oxygen, nitrogen or sulfurare also included in the term “hydrocarbyl”.

The term “hydrocarbylene” in the context of the present invention refersto a linear, branched or cyclic alkylene, vinylene, arylene, aralkyleneor alkarylene of 1 to 120 carbon atoms, and substituted derivativesthereof. The substituent group can be halogen, hydroxy, hydrocarbyloxy,carboxyl, ester, ketone, cyano, amino, amido and nitro groups.Hydrocarbylene groups in which the carbon chain is interrupted byoxygen, nitrogen or sulfur are also included in the term“hydrocarbylene”.

The present invention includes a radiation imageable element comprisinga hydrophilic, porous oxide base, which is overcoated with animage-forming layer comprising polymer particles. The ratio of theaverage surface oxide pore diameter of the hydrophilic base to theaverage particle diameter of the polymer particles is from about 0.4:1to about 10:1, preferably 0.4:1 to 10:1, more preferably, the ratio isfrom about 0.5:1 to about 5:1. Radiation can be a photo, thermal orelectron beam radiation.

The term “particle” in the context of the present invention refers to asolid, which is dispersed in a continuous phase.

Preferably, the pores have an average pore diameter from about 10 toabout 100 nm, more preferably, from about 10 to about 75 nm.

Preferably, the polymer particles have an average particle diameter fromabout 1 to about 250 nm, more preferably, from about 10 to about 200 nm.

The support material comprises an aluminum or aluminum alloy plate.Suitable aluminum alloys include alloys with zinc, silicon, chromium,copper, manganese, magnesium, chromium, zinc, lead, bismuth, nickel,iron or titanium which may contain negligible amounts of impurities.Preferred plates have a thickness of about 0.06 to about 0.6millimeters.

The surface of the aluminum plate is preferably subjected to chemicalcleaning such as degreasing with solvents or alkaline agents for thepurpose of exposing a clean surface free of grease, rust or dust whichis usually present on the aluminum surface. Preferably, the surface isgrained. Suitable graining methods include glass bead graining, quartzslurry graining, ball graining, the blasting, brush graining andelectrolytic graining. Following the graining operation, the support canbe treated with an aluminum etching agent and/or a desmutting acid bath.

In a preferred embodiment, the ratio of the average surface oxide porediameter of the hydrophilic base to the average particle diameter of thepolymer particles is from about 0.8:1 to about 10:1 and the incidentexposure dose is not more than about 340 mJ/cm². More preferably, thepore size/particle size ratio is from about 1.0:1 to about 10:1 and theincident exposure dose is not more than about 300 mJ/cm².

Preferably, the porous oxide base comprises anodized aluminum; theelement is free of an interlayer between the porous anodized aluminumbase and the image forming layer; the image forming layer also comprisesa photothermal conversion material; the heat sensitive polymer particleshave a glass transition temperature of at least 50° C., preferably 60°C.; and the image forming layer is negative working.

In another preferred embodiment, the present invention includes aradiation imageable element the ratio of the average surface oxide porediameter of the hydrophilic base to the average particle diameter of thepolymer particles is from about 0.6:1 to about 10:1 and the radiationimageable element is free of an interlayer between the porous anodizedaluminum base and the image forming layer.

The porous oxide base is preferably an aluminum sheet comprising atleast one anodically oxidized surface. In general, any known method ofanodic oxidation, followed by etching, if necessary, that can provide anappropriate pore diameter corresponding to the polymer particles, may beused to prepare the aluminum base.

Anodic pore size for sulfuric acid anodization is typically less than 20nm whereas anodic pore size for phosphoric acid anodization is typicallygreater than 30 nm. Typically, lithographic printing plates utilize analuminum base, which is anodized in sulfuric acid, wherein the averageoxide pore size is about 15 nm in diameter. However, phosphoric acid canbe used instead of sulfuric acid. Phosphoric acid provides larger anodicpore size and enhances adhesion of photopolymer compositions. The use oflarge anodic pore substrates that are phosphoric acid anodized ispreferred over sulfuric acid-anodized substrates. Other conventionalanodization methods can also be used in the preparation of the anodizedsubstrate of the present invention, including particularly those thatproduce an anodic pore size larger than anodic pore size produced bysulfuric acid anodization.

Thus, preparation of the anodically oxidized surface can be accomplishedby anodically oxidizing the aluminum sheet in an aqueous phosphoric orsulfuric acid solution to produce an oxide layer. The anodic oxidationis optionally followed by etching of the the oxide layer to a fractionof its original thickness, such as, for example, to about ½ of itsoriginal thickness. Alternatively, a lithographic printing plateprecursor can be prepared by the above method.

The anodised aluminum support may be treated to improve the hydrophilicproperties of its surface. For example, the aluminum support may besilicated by treating its surface with sodium silicate solution atelevated temperature, e.g., 95° C. Alternatively, a phosphate treatmentmay be applied which involves treating the aluminum oxide surface with aphosphate solution that may further contain an inorganic fluoride.Further, the aluminum oxide surface may be rinsed with a citric acid orcitrate solution. This treatment may be carried out at room temperatureor can be carried out at a slightly elevated temperature of about 30 to50° C. A further treatment can include rinsing the aluminum oxidesurface with a bicarbonate solution. It is evident that one or more ofthese post treatments may be carried out alone or in combination.

Examples of the aluminum or aluminum alloy plate of the inventioninclude a plate of pure aluminum and a plate of aluminum alloy withother metal such as silicon, copper, manganese, magnesium, chromium,zinc, lead, bismuth and nickel. The plate in the form of a sheet ispreferably used. The aluminum or aluminum alloy plate is preferablygrained before the anodic oxidation treatment by the conventionalmanner, such as brush (mechanical) graining, chemical graining,electrolytic graining and the like. Furthermore, after the anodicoxidation treatment, it may be optionally hydrophilized.

The oxide base comprises oxides and phosphates of aluminum and ispresent in a coverage of greater than 100 milligrams per square meter ofthe hydrophilic anodized aluminum base, preferably, greater than 500milligrams per square meter of the hydrophilic anodized aluminum base.Preferably, the oxide base has a average thickness of at least 0.40micrometers.

In accordance with the present invention, on top of a hydrophilicsurface there is provided a radiation-sensitive image forming layer.Various materials suitable for forming images for use in thelithographic printing process can be used. Any suitable radiationimageable layer, which after exposure and subsequent development, ifnecessary, can provide an area in imagewise distribution suitable forprinting can be used.

Thus, the image forming layer according to the present inventioncomprises polymer particles, and can further comprise pigments. Thepolymer particles can be a thermoplastic polymer or thermoset polymer.The thermoplastic polymer can be a hydrophobic polymer or a polymer thathas both hydrophobic and hydrophilic segments thereon, such as a graftpolymer or copolymer. The thermoset polymer can be a latex particle.

Examples of the polymer particles include:

(1) a thermoplastic homopolymer or copolymer formed from polymerizationof one or more monomers selected from: acrylic acid, methacrylic acid,acrylamide, methacrylamide, ester of acrylic acid, ester of methacrylicacid, hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide,methacrylamide, N-hydroxyethyl acrylamide, N-hydroxyethylmethacrylamide, styrene, p-hydroxystyrene, α-methylstyrene,p-methylstyrene, vinyl acetate, methyl vinyl ether, ethyl vinyl ether,hydroxyethyl vinyl ether, vinylphosphonic acid, vinyl chloride,vinylidene chloride, acrylonitrile, N-vinyl pyrrolidone and N-vinylcarbazole;

(2) a thermoset polymer, such as, a phenol-formaldehyde resin, acresol-formaldehyde resin, melamine-formaldehyde resin, a polyurethaneresin and a combination thereof;

(3) a graft polymer having hydrophilic and hydrophobic segments, suchas, a graft polymer or copolymer having a hydrophobic polymer backboneand a plurality of pendant groups represented by the formula:

-Q-W-Y

wherein Q is a difunctional connecting group; W is selected from thegroup consisting of: a hydrophilic segment and a hydrophobic segment; Yis selected from the group consisting of: a hydrophilic segment and ahydrophobic segment; with the proviso that when W is a hydrophilicsegment, Y is selected from the group consisting of: a hydrophilicsegment and a hydrophobic segment, with the further proviso that when Wis hydrophobic, Y is a hydrophilic segment.

Specific examples of polymer particles for use in connection with thepresent invention include polystyrene, polyvinyl chloride, polyvinylacetate, polymethyl methacrylate, polyvinylidene chloride, polyvinylcarbazole, polyacrylonitrile, graft polymer and copolymer particles andmixtures thereof.

The graft copolymer is a thermally sensitive polymer having ahydrophobic polymer backbone and a plurality of pendant groupsrepresented by the formula:

-Q-W-Y

wherein Q is a difunctional connecting group; W is selected from thegroup consisting of: a hydrophilic segment and a hydrophobic segment; Yis selected from the group consisting of: a hydrophilic segment and ahydrophobic segment; with the proviso that when W is a hydrophilicsegment, Y is selected from the group consisting of: a hydrophilicsegment and a hydrophobic segment, with the further proviso that when Wis hydrophobic, Y is a hydrophilic segment.

Preferably, the thermally sensitive graft copolymer comprises repeatingunits represented by the formula:

wherein each of R¹ and R² can independently be H, alkyl, aryl, aralkyl,alkaryl, COOR⁵, R⁶CO, halogen or cyano.

Q can be one of:

wherein R³ can be H or alkyl; R⁴ can independently be H, alkyl, halogen,cyano, nitro, alkoxy, alkoxycarbonyl, acyl or a combination thereof.

The segment W can be a hydrophilic segment or a hydrophobic segment,wherein the hydrophilic segment can be a segment represented by theformula:

wherein each of R⁷, R⁸, R⁹ and R¹ can independently be H or methyl; R³can be H and alkyl; and wherein the hydrophobic segment can be —R¹²—,—O—R¹²—O—, —R³N—R¹²—NR³—, —OOC—R¹²—O— or —OOC—R¹²—O—, wherein each R¹²can independently be a linear, branched or cyclic alkylene of 6-120carbon atoms, a haloalkylene of 6-120 carbon atoms, an arylene of 6-120carbon atoms, an alkarylene of 6-120 carbon atoms or an aralkylene of6-120 carbon atoms; R³ can be H or alkyl.

Y can be a hydrophilic segment or a hydrophobic segment, wherein thehydrophilic segment can be H, R¹⁵, OH, OR¹⁶, COOH, COOR¹⁶, O₂CR¹⁶, asegment represented by the formula:

wherein each of R⁷, R⁸, R⁹ and R¹⁰ can independently be H or methyl; R³can be H and alkyl; wherein each R¹³, R¹⁴, R¹⁵ and R¹⁶ can be H or alkylof 1-5 carbon atoms and wherein the hydrophobic segment can be a linear,branched or cyclic alkyl of 6-120 carbon atoms, a haloalkyl of 6-120carbon atoms, an aryl of 6-120 carbon atoms, an alkaryl of 6-120 carbonatoms, an aralkyl of 6-120 carbon atoms, OR¹⁷, COOR¹⁷ or O₂CR¹⁷, whereinR¹⁷ can be an alkyl of 6-20 carbon atoms.

Z can be H, alkyl, halogen, cyano, hydroxy, alkoxy, alkoxycarbonyl,hydroxyalkyloxycarbonyl, acyl, aminocarbonyl, aryl and substituted aryl;

j is at least 1;

k is at least 1;

m is at least 2; and

n is from 1 to about 500; with the proviso that when W is a hydrophilicsegment, Y is a hydrophilic segment or a hydrophobic segment, with thefurther proviso that when W is hydrophobic, Y is a hydrophilic segment.The substituent in the above substituted aryl can be alkyl, halogen,cyano, alkoxy or alkoxycarbonyl. Preferably, the alkyl group is an alkylof 1 to 22 carbon atoms.

In another preferred embodiment, the segment W-Y can be represented bythe formula:

—(OCH₂CH₂)_(n)—OCH₃

wherein n is from 25 to about 75. In this preferred embodiment, thethermally sensitive graft copolymer has, for example, repeating unitsrepresented by the formula:

wherein j and k are each at least 1; m is at least 5; and n is from 25to about 75. More preferably, n has an average value of about 45.

In another preferred embodiment, the thermally sensitive graft copolymercomprises repeating units represented by the formula:

wherein j and k are each at least 1; m is at least 5; and n is from 25to about 75, more preferably, n has an average value of about 45.

The thermally sensitive graft copolymer having hydrophobic and/orhydrophilic segments can be prepared by known methods.

Other materials that can be useful in this invention include systemsthat are well known in the art, and include silver halide emulsions, asdescribed in Research Disclosure, publication 17643, paragraph XXV,December, 1978, and references cited therein; polymeric and nonpolymericquinone diazides as described in U.S. Pat. No. 4,141,733 and referencescited therein; light sensitive polycarbonates, as described in U.S. Pat.No. 3,511,611 and references cited therein; diazonium salts, diazoresins, cinnamal-malonic acids and functional equivalents thereof andothers described in U.S. Pat. No. 3,342,601 and reference cited therein;light sensitive polyesters, polycarbonates and polysulfonates, asdescribed in U.S. Pat. No. 4,139,390 and references cited therein; andthe materials described in the commonly owned U.S. Pat. No. 4,865,951.The contents of these patents are incorporated by reference as fully setforth herein.

Although a negative image formed by thermal coalescence of a heatsensitive polymer is described in the examples that follow, any photo orthermal process, either positive working or negative working, in whichpolymer particles are involved in the formation of an image is expectedto benefit from the present invention. Such processes can includenegative working systems wherein, for example, polymer particles arethermally ruptured to produce a crosslinking agent or a reactant. Theycan also include positive working systems wherein, for example,thermally ruptured polymer particles release a reactant or catalystwhich solubilizes a polymer by converting hydrophobic groups intohydrophilic groups, as is the case in the acid-catalyzed unblocking ofacid labile esters to produce carboxylic or sulfonic acids. Thus, thepresent invention can be used in any photo or thermal imagingapplication.

The polymer particles used in connection with the present invention havea glass transition temperature of at least 40° C., more preferably of atleast 50° C. and preferably have a coagulation temperature above 40° C.,more preferably of at least 60° C. Coagulation may result from softeningor melting of the thermoplastic polymer or graft copolymer particlesunder the influence of heat. There is no specific upper limit to thecoagulation temperature of the polymer particles, however thetemperature should be sufficiently below the decomposition of thepolymer particles. Preferably, the coagulation temperature is at least10° C. below the temperature at which the decomposition of the polymerparticles occurs. When the polymer particles are subjected to atemperature above coagulation temperature they coagulate to form anagglomerate, which becomes insoluble in aqueous developer.

Preferably, the Number Average Molecular Weight of the polymers,including the graft copolymers, is from about 2,000 to about 2,000,000and a glass transition temperature of at least 40° C., more preferably,from about 50° C. to about 150° C.

The amount of polymer particles contained in the image forming layer ispreferably between 20% by weight and 65% by weight and more preferablybetween 25% by weight and 55% by weight and most preferably between 30%by weight and 45% by weight.

The polymer particles can be present as a dispersion in the aqueouscoating liquid of the image forming layer. An aqueous dispersion of thethermoplastic polymer particles can be prepared by dissolving thethermoplastic polymer in an organic, water immiscible solvent,dispersing the thus obtained solution in water or in an aqueous medium,and removing the organic solvent by evaporation.

Examples of the pigments include: carbon blacks, metal carbides,borides, nitrides, carbonitrides and bronze-structured oxides. Suchpigments may absorb radiation in the ultraviolet, visible or infraredspectral regions and may also function as light to heat convertingcompounds in the present invention.

A light to heat converting compound in connection with the presentinvention can be preferably added to the image forming layer but atleast part of the light to heat converting compound may also be includedin a neighbouring layer, if such a layer is present.

Suitable compounds capable of converting light into heat are preferablyinfrared absorbing components although the wavelength of absorption isnot of particular importance as long as the absorption of the compoundused is in the wavelength range of the light source used for image-wiseexposure. Particularly useful compounds are for example dyes and inparticular infrared dyes and carbon black. The lithographic performanceand in particular the print endurance obtained depends on theheat-sensitivity of the imaging element. In this respect it has beenfound that carbon black yields favorable results.

Classes of materials that are useful as photothermal converters include,but are not limited to, squarylium, croconate, cyanine (includingphthalocyanine), merocyanine, chalcogenopyryloarylidene, bis(chalcogenopyrylo) polymethine, oxyindolizine, quinoid, indolizine,pyrylium and metal thiolene dyes or pigments. Other useful classesinclude thiazine, azulenium and xanthene dyes. Still other usefulclasses are carbon blacks, metal carbides, borides, nitrides,carbonitrides and bronze-structured oxides. Particularly useful asphotothermal converters are infrared absorbing dyes of the cyanineclass.

The amount of infrared absorbing compound in the image forming layer isgenerally sufficient to provide an optical density of at least 0.5 inthe layer and, preferably, an optical density of from about 1 to about3. This range would accommodate a wide variety of compounds havingvastly different extinction coefficients. Generally, this is at least 1weight percent and, preferably, from about 5 to about 30 weight percent.

An imaged element according to the present invention can be producedwith or without a development step.

In the first instance, the method of producing an imaged element of thepresent invention comprises the steps of:

providing a radiation-imageable element for lithographic printingcomprising: a hydrophilic anodized aluminum base having a surfacecomprising pores; and coated thereon an image-forming layer comprisingpolymer particles, the ratio of the average pore diameter to the averageparticle diameter being from about 0.4:1 to about 10:1;

imagewise exposing the radiation-imageable element to radiation toproduce exposed and unexposed regions; and

contacting the imagewise exposed radiation-imageable element and adeveloper to selectively remove said exposed or said unexposed regions.

In the second instance, the method of producing an imaged element of thepresent invention comprises the steps of:

providing a radiation-imageable element for lithographic printingcomprising: a hydrophilic anodized aluminum base having a surfacecomprising pores; and coated thereon an image-forming layer comprisingpolymer particles, the ratio of the average pore diameter to the averageparticle diameter being from about 0.4:1 to about 10:1; and

imagewise exposing the radiation-imageable element to radiation toproduce exposed and unexposed regions.

The lithographic printing plate of the present invention can be exposedby conventional methods, for example through a transparency or astencil, to an imagewise pattern of actinic radiation. Suitableradiation sources include sources rich in visible radiation and sourcesrich in ultraviolet radiation. Carbon arc lamps, mercury vapor lamps,fluorescent lamps, tungsten filament lamps, photoflood lamps, lasers andthe like are useful herein. The exposure can be by contact printingtechniques, by lens projection, by reflex, by bireflex, from animage-bearing original or by any other known technique.

Typically, the step of exposing the imageable element to thermalradiation is carried out using an infrared laser. However, other methodssuch as visible or UV laser imaging may also be used, provided that aphotoconverter, i.e., a photothermal converter, is present. Thus, forexposure with such visible or UV radiation sources, the imageablecomposition generally includes a photothermal converting material.Alternatively, the imageable element of the present invention can beimaged using a conventional apparatus containing a thermal printing heador any other means for imagewise conductively heating the imageablecomposition, such as, with a heated stylus or with a heated stamp.

The imagewise exposure of the imageable element to thermal radiation iscarried out using an exposure dose sufficient for imaging. Typically, anincident exposure dose of from about 50 to about 1000 mJ/cm² is used inthermal imaging. Preferably, the incident exposure dose is not more than600 mJ/cm², more preferably, the incident exposure dose is not more than400 mJ/cm² and most preferably, the incident exposure dose is not morethan 300 mJ/cm².

The step of exposure of the imageable element to thermal radiation isfollowed by a development step preferably using an aqueous developer.The aqueous developer composition is dependent on the nature of thecomposition of the polymer particles. Common components of aqueousdevelopers include surfactants, chelating agents, such as salts ofethylenediamine tetraacetic acid, organic solvents, such as benzylalcohol, and alkaline components, such as, inorganic metasilicates,organic metasilicates, hydroxides and bicarbonates. The pH of theaqueous developer is preferably within about 5 to about 14, depending onthe nature of the composition of the polymer particles.

For the development step, a diluted alkaline solution optionallycontaining preferably up to 10% by volume of organic solvent may beused. Examples of alkaline compound include inorganic compound such assodium hydroxide, potassium hydroxide, lithium hydroxide, sodiumsilicate and sodium bicarbonate, and organic compound such as ammonia,monoethanolamine, diethanolamine and triethanolamine. Preferableexamples of water-soluble organic solvent include isopropyl alcohol,benzyl alcohol, ethyl cellosolve, butyl cellosolve, diacetone alcoholand the like. The developing solution may contain a surfactant, dye,salt for inhibiting the swelling or salt for corroding the metalsubstrate.

Following development, a postbake may optionally be used to increasepress life. In the practice of the present invention, a post-exposure,pre-development heat step may also be used. This pre-development heatstep can further aid in increasing differentiation between exposed andunexposed areas.

In addition to the imageable layer, the imageable element can haveadditional layers, such as, an overlying layer. Possible functions of anoverlying layer include:

(1) to prevent damage, such as scratching, of the surface layer duringhandling prior to imagewise exposure; and

(2) to prevent damage to the surface of the imagewise exposed areas, forexample, by over-exposure which could result in partial ablation.

The overlying layer should be soluble, dispersible or at least permeableto the developer.

The present invention enhances interaction of the image-forming layerwith the substrate surface layer, thereby enhancing press life. Theresults suggest that, if the heat sensitive particles are able to enterinto the oxide pores of the substrate, an enhanced adhesion would resultfollowing imaging.

Lithographic plates prepared by photochemical processes in whichphotopolymerizable polymer particles are employed in image formation,such as the no-process plate described in U.S. Pat. No. 5,922,507, areexpected to benefit from this substrate oxide pore-size/imaging layerparticle size matching described in the present invention. In addition,photo and thermal imaging compositions, in which polymer particles arenot involved in image formation, but rather are used to reinforce andenhance durability of the image, can also benefit from this approach.

The present invention provides average pore diameter to average particlediameter ratios that can enhance the interaction of the image-forminglayer with the substrate surface layer following thermal imaging byallowing the polymer particles to enter into the oxide pores of thesubstrate, thereby enhancing adhesion. The enhanced adhesion, in turn,will enhance the sensitivity and the press life of the printing plates.

Without being bound by any theory, it is believed that the ability ofthe polymer particles to enter the oxide pores enhances adhesion of theimageable layer to the anodized aluminum base following thermal or photoimaging. Thus, including an interlayer between the imageable layer tothe anodized aluminum base would reduce the ability of the particles toenter the pores and increasing the incident exposure dose would enhancethe ability of the particles to enter the pores.

The present invention provides a radiation imageable composition that isuseful in photo or thermal imaging of, for example, lithographic platesand printed circuit boards.

The invention is further described in the following examples, which areintended to be illustrative and not limiting.

EXAMPLE 1

A polystyrene-co-poly (acrylic acid) latex having an average particlediameter of 37 nm was synthesized as follows. A mix of initiator(ammonium persulfate, 1.6 g) and surfactant (sodium dodecyl sulfate, 3.0g) in distilled water (520 g) was stirred mechanically with aglass-Teflon stirrer in a 1 L round bottom flask under N₂ and heated to70° C. The monomer mixture (styrene, 137 g, and acrylic acid, 13.5 g)was added over 3-4 hr, after which the polymerization was allowed tocontinue for an additional 2-3 hr. The resulting latex was dialyzedagainst distilled water containing a small amount of ammonium hydroxideto remove the excess sodium dodecyl sulfate. The latex particlediameters were measured on a Microtac Ultrafine Particle Analyzer at 25°C. and were in the range of about 30-40 nm, with an average diameter ofabout 37 nm.

EXAMPLE 2

A polystyrene-co-poly (acrylic acid) latex having an average particlediameter of about 15 nm was synthesized as follows. The procedure ofexample 1 was repeated except that 38.0 g of sodium dodecyl sulfate wasused in place of 3.0 g of the surfactant. Following prolonged dialysisto remove excess surfactant, the latex particle diameters were found tobe in the range of about 10-20 nm, with an average diameter of about 15nm.

EXAMPLE 3

The polystyrene-co-poly (acrylic acid) latex of Example 2 (15 g) wasdiluted in distilled water (450 g), stirred mechanically under N₂ andheated to 70° C. in a 1-L round bottom flask. A solution of ammoniumpersulfate (2 g) in distilled water (15 g) was added, followed by thedropwise addition of styrene (165 g) over 3 hr. The polymerizationmixture was heated at 70° C. for an additional 2 hr and allowed to coolto room temperature, after which aqueous 30% ammonium hydroxide (20 g)was added. The latex particles were estimated to have an averagediameter of about 60 nm, based on the ratio of monomer to surfactantutilized.

EXAMPLE 4

A carbon black dispersion was prepared as follows. A solvent mix ofdistilled water (4.5 kg), 2-propanol (6.0 kg) and ammonium hydroxide(28-30% ammonia) (1.5 kg) was prepared. One third of the solvent mixturewas placed in a blender to which carbon black CWA (55% pigment,available from Ciba) (3 kg) was slowly added with mechanical stirring.Stirring was continued for 10 min, after which the mixture was dilutedto 40% solids with the above solvent mix and passed through a shot millfor three consecutive times. Subsequently, the dispersion was furtherdiluted with the remaining solvent mix to provide about 20% solids. Theaverage particle diameter of the carbon black was about 250 nm.

EXAMPLE 5

Thermally sensitive coating formulations of the carbon black dispersionwith each of the above latexes were prepared as follows. The carbonblack dispersion of Example 4 (20.7% solids) (24.2 g) was mixed with thelatex of example 1 (11.5% solids) (71.3 g); the mixture was stirred for30 min and filtered to provide coating-1, which contains latex particleshaving an average diameter of about 37 nm.

In a similar manner, the carbon black dispersion was mixed with thelatex of Example 2 to provide coating-2 and the latex of Example 3 toprovide coating-3. Coating-2 and coating-3 contain latex particleshaving an average diameter of about 15 nm and about 60 nm, respectively.

EXAMPLE 6

Thermally sensitive printing plates were prepared and press tested asfollows. Aluminum sheets were electrolytically grained in 1%hydrochloric acid, alkaline washed to remove the smut, and then anodizedin 20% sulfuric acid at 30-40° C. to provide an oxide weight of 2.5g/m². The porous anodic oxide surface exhibited average pore diametersin the range of about 10-20 nm.

One of the anodized sheets was post-treated with a sodium silicatesolution to provide a silicate interlayer. Another of the sheets waspost-treated with a polyvinyl phosphonic acid (PVPA) solution to providea PVPA interlayer. Coating-1, which contains latex particles havingaverage diameters of about 37 nm, as described in Example 4, wasspin-coated on each of these bases to provide coating weights of 1.2g/m². A third sheet was directly spin-coated with coating-1 with nopost-anodic interlayer.

The coated bases were imagewise exposed in a Creo Trendsetter 3244imagesetter, utilizing a laser diode array emitting at 830 nm. A powersetting of 10.5 W and variable drum speeds were used to expose each ofthe plate precursors in increments of 20 mJ/cm² between 200 and 320mJ/cm². The exposed plate precursors were subsequently developed usingdeveloper 955 (available from Kodak Polychrome Graphics) and mounted ona sheet-fed printing press. In both cases, for exposure doses less than280 mJ/cm², the exposed image area was removed during development. Theplates exposed to higher exposure doses were mounted on a sheet-fedprinting press.

Less than 100 clean impressions of poor image quality were obtained.

EXAMPLE 7

The silicated anodized sheet of Example 6 was soaked in 5% citric acidfor 3 minutes, followed by 3 consecutive rinses with deionized water, toprovide an acid-washed silicated base, which was spin-coated withcoating-1, as described in Example 6.

The resulting coated base and the coated bases of Example 6 wereimagewise exposed in the Creo 3244 imagesetter between 340-460 mJ/cm² in20 mJ/cm² increments, developed and mounted on a sheet-fed printingplate, as described in Example 6.

Less than 100 clean impressions of poor image quality were obtained withthe plates, which were interlayered with silicate and PVPA. However,more than 10,000 good impressions were obtained with the plates havingno interlayer and the acid-washed silicate interlayer at the higherexposure dose ranges.

The results of Examples of 6 and 7, together with those of thesubsequent reactions are summarized in Table 1.

TABLE 1 Summary of Results¹ Anodizing acid: Pore Average Average size/pore particle Clean particle size size Dose Impres- size Ex (nm)Interlayer (nm) (mJ/cm²) sions ratio 6 Sulfuric: 15 Silicate 37 200-<100 0.40 320 6 Sulfuric: 15 PVPA 37 200- <100 0.40 320 6 Sulfuric: 15None 37 200- <100 0.40 320 7 Sulfuric: 15 Silicate 37 340- <100 0.40 4607 Sulfuric: 15 PVPA 37 340- <100 0.40 460 7 Sulfuric: 15 None 37340- >10,000 0.40 460 7 Sulfuric: 15 Silicate 37 340- >10,000 0.40 Acid460 Washed 8 Sulfuric: 15 Silicate 15 340- >10,000 1.0 460 8 Sulfuric:15 PVPA 15 340- >10,000 1.0 460 8 Sulfuric: 15 None 15 340- >10,000 1.0460 9 Phosphoric: 37 Polyacry- 37 200- 100,000 1.0 lic acid 320 9Phosphoric: 37 None 37 200- 120,000 1.0 320 9 Phosphoric: 37 None 15200- 150,000 2.5 320 11 Phosphoric: 37 Polyacry- 60 260- <100 0.62 licacid 340 11 Phosphoric: 37 None 60 260- <100 0.62 340 11 Phosphoric: 37Polyacry- 60 380- 100,000 0.62 lic acid 460 11 Phosphoric: 37 None 60380- 100,000 0.62 460 12 Sulfuric Silicate 37 200- 120,000 0.95(phospho-ric 320 etch): 35 12 Sulfuric PVPA 37 200- 120,000 0.95(phospho-ric 320 etch: 35 12 Sulfuric None 37 200- 120,000 0.95(phospho-ric 320 etch): 35 13 Sulfuric Silicate 30 240- <1000 0.67(phosphor-ic 320 etch) sulfuric: 20 13 Sulfuric PVPA 30 240- <1000 0.67(phosphor ic 320 etch) sulfuric: 20 13 Sulfuric None 30 240- 100,0000.67 (phosphoric 320 etch) sulfuric: 20 15 Sulfuric Silicate 30 240-50,000 1.2 (phosphoric 320 etch) phosphoric: 35 15 Sulfuric PVPA 30 240-50,000 1.2 (phosphoric 320 etch) phosphoric: 35 15 Sulfuric None 30 240-90,000 1.2 (phosphoric 320 etch) phosphoric: 35 ¹Examples 6-9, 11 and 12utilize coating-1, coating-2 or coating-3, described in Example 5.Examples 13 and 15 utilize coating-4, described in Example 14.

EXAMPLE 8

Anodized sheets of Example 6 and 7, with no interlayer, as well as withsilicate, PVPA and acid-washed silicate interlayer, were spin-coatedwith coating-2, which contains latex particles having average particlediameters of about 15 nm, to provide coating weights of 1.2 g/m². Eachof these 4 bases was then imagewise exposed, developed and mounted on asheet-fed printing press as described in Example 6. All plates, whichwere exposed at the higher doses of 340-460 mJ/cm², provided more than10,000 good impressions on press.

EXAMPLE 9

Thermally sensitive printing plate precursors were prepared and presstested as follows. Aluminum sheets were slurry grained, alkaline etched,desmutted and anodized in a 20% phosphoric acid solution at 30-40° C. toprovide an oxide weight of 1.7 g/m². The porous anodic surface exhibitedaverage pore diameters in the range of about 35-40 nm. One of theanodized sheets was spin-coated with coating-1; another of the anodizedsheets was spin-coated with coating-2. A third of the anodized sheetswas treated with a polyacrylic acid (PAA) interlayer, prior to beingspin-coated with coating-1. Each of the coated bases was imagewiseexposed at 200-320 mJ/cm², developed and mounted on a sheet-fed printingpress, as in example 6. The PAA interlayered and non-interlayeredcoating-1 plates, which contain 37-nm particles, provided about 100,000and 120,000 clean impressions, respectively. About 150,000 cleanimpressions were obtained with the non-interlayered, coating-2 plate,which contains 15-nm particles.

EXAMPLE 10

Thermally sensitive lithographic printing plates, utilizing coating-1and no interlayer, were prepared and press tested as described inexample 9, except that the anodization time was varied to provide oxideweights of 1.7-2.5 g/m². About 125,000 clean impressions were obtainedin each case.

EXAMPLE 11

Anodized sheets, described in Example 9, with and without PAAinterlayer, were spin-coated with coating-3, which contains latexparticles having average particle diameters of about 60 nm, imagewiseexposed at 260-340 mJ/cm², developed and mounted on a sheet-fed printingpress, as in Example 6. Less than 100 clean impressions of poor imagequality were obtained with both plates with and without the PAAinterlayer. The coated bases of Example 11 were imagewise exposed in theCreo 3244 imagesetter between 380-460 mJ/cm² in 20 mJ/cm² increments,developed and mounted on a sheet-fed printing plate, as described inExample 6. Both plates, which were imagewise exposed at the higher doseranges, provided about 100,000 good impressions.

EXAMPLE 12

Thermally sensitive lithographic printing plates were prepared and presstested as described in Example 5, except that the aluminum sheets wereslurry grained and the anodization time in 20% sulfuric acid solutionwas varied to provide oxide weights of 2.8 to 15 g/m². As in Example 5,the porous anodic surface exhibited average pore diameters in the rangeof about 10-20 nm. In each case, the anodized bases were then etched toabout half of the original oxide weight, which resulted in an increaseof surface oxide pore diameters by a factor of about 2. The etchingprocess was carried out either in aqueous alkaline solution (5% sodiumhydroxide) or in acidic solution (20% phosphoric acid). Coating-1 wasthen spin-coated on these bases, followed by imagewise exposure,development and press testing, as described in example 6. Each of theresulting plates provided about 120,000 clean impressions for exposureswithin the range of 200-320 mJ/cm².

Example 12 demonstrates that oxide pore size can be increased to providelong-running printing plates by a post anodic etch process. The averageoxide pore size was in the range of about 30-40 nm. These experimentsalso demonstrate that the process of etching the anodized bases to abouthalf of their original oxide weight provided optimal press life.

EXAMPLE 13

Thermally sensitive lithographic printing plates were prepared and presstested as follows. Aluminum sheets were electrolytically grained in 1-%hydrochloric acid, alkaline washed to remove the smut, and then anodizedin 20% sulfuric acid at 30-40° C. to provide an oxide weight of 2.5g/m², as described in Example 6. The porous anodic surface exhibitedaverage pore diameters in the range of about 10-20 nm. Most of the oxidelayer was etched with 20% phosphoric acid solution, followed byre-anodization in 20% sulfuric acid solution to provide an average poresize in the range of about 10-30 nm. One of the anodized sheets washydrophilized with a sodium silicate solution. Another of the sheets wasinterlayered with a PVPA solution. Coating-4, which contains latexparticles having average diameters of about 30 nm, as described inExample 14, was bar-coated onto each of these interlayered-bases, aswell directly onto a base with no interlayer, to provide a coatingweights of 2.0 g/m². The coated bases were imagewise exposed in a CreoTrendsetter 3244 imagesetter, utilizing a laser diode array emitting at830 nm. A power setting of 10.5 W and variable drum speeds were used toexpose each of the plate precursors in increments of 40 mJ/cm² between240 and 320 mJ/cm². The exposed plate precursors were subsequentlydeveloped using developer 955 or Scorpio (both available from KodakPolychrome Graphics) and mounted on a sheet-fed printing press. Lessthan 1,000 clean impressions were obtained with both of the interlayeredplates, owing primarily to loss of adhesion. However, the plate with nointerlayer provided about 100,000 clean impressions for exposures of 280and 320 mJ/cm².

EXAMPLE 14

Coating-4 was prepared as follows. Acrylic resin solution ACR-1412(described below) (5 g of a 40 wt % solution) was dissolved in methanol(10.8 g) by stirring for 15 min, followed by the addition of an aqueousammonium hydroxide solution (0.39 g, 28 wt %) to neutralize the resin.Subsequently, an aqueous solution of IR dye, ADS-825WS (available fromAmerican Dye Source) (0.32 g dye dissolved in 26.8 g distilled water),was added. After stirring for 15 min, latex dispersion ACR-1410(described below) (6.72 g) was slowly added, followed by stirring for anadditional 30 min. Acrylic resin ACR-1412 was prepared as follows. Amixture of methyl methacrylate (19.1 g), methacrylic acid (3.3 g), ethylacrylate (2.5 g), azoisobutyronitrile (0.5 g) and dodecylmercaptan (0.09g) was heated at 80° C. in 2-methoxyethanol (153 g) under nitrogen, in areaction vessel equipped with a dropping funnel and reflux condenser.Subsequently, a mixture of methyl methacrylate (57.4 g), methacrylicacid (10.2 g), ethyl acrylate (7.5 g), azoisobutyronitrile (1 g) anddodecylmercaptan (0.19 g) was added over a period of 2 hrs, followed byadditional azoisobutyronitrile (0.25 g). After heating at 80° C. for 2hrs, more azoisobutyronitrile (0.25 g) was added, follow by heating foran additional 2 hrs, after which the reaction was allowed to cool toroom temperature. The acid number of the terpolymer of methylmethacrylate, methacrylic acid and ethyl acrylate was 88. Acrylic latexACR-1410 was prepared as follows. A mix of initiator (potassiumpersulfate, 1.0 g), surfactant (sodium dodecyl sulfate, 1.0 g) andsodium bicarbonate (0.5 g) in distilled water (617 g) was stirred undernitrogen for 15 minutes at room temperature, followed by heating at 80°C. for 30-45 min. Methyl methacrylate (200 g) was added over a period of90 min. After 1 hr, the reaction was complete, based on % non-volatiles.The reaction was heated for an additional 30 min. Brookfield viscosityat 25° C. was 30 cps; latex particle diameters were in the range ofabout 25-35 nm, as determined with a Microtac Utraline ParticleAnalyzer.

EXAMPLE 15

Thermally sensitive lithographic printing plates were prepared and presstested as described in Example 13 except that, following the etchingstep with 20% phosphoric acid solution, the aluminum base wasre-anodized in 20% phosphoric acid solution. The average oxide pore sizewas in the range of about 30-40 nm. One of the anodized sheets washydrophilized with a sodium silicate solution. Another of the sheets wasinterlayered with a PVPA solution. Coating-4 was bar-coated onto each ofthese interlayered-bases, as well directly onto a base with nointerlayer, to provide coating weights of 2.0 g/m², followed byimagewise exposure, development and mounting on a sheet-fed printingpress, as described in Example 12. The plates interlayered with silicateand PVPA each provided about 50,000 impressions clean impressions forexposures of 240 and 280 mJ/cm². The plate with no interlayer providedabout 90,000 clean impressions for exposures of 280 and 320 mJ/cm².

The present invention has been described with particular reference tothe preferred embodiments. It should be understood that variations andmodifications thereof can be devised by those skilled in the art withoutdeparting from the spirit and scope of the present invention.Accordingly, the present invention embraces all such alternatives,modifications and variations that fall within the scope of the appendedclaims.

What is claimed is:
 1. A radiation-imageable element for lithographicprinting comprising: a hydrophilic anodized aluminum base having asurface comprising pores characterized by an average pore diameter; andcoated thereon an image-forming layer comprising polymer particlescharacterized by an average particle diameter, the ratio of said averagepore diameter to said average particle diameter being from 0.4:1 to10:1.
 2. The radiation-imageable element of claim 1, wherein saidaverage pore diameter to said average particle diameter ratio is fromabout 0.5:1 to about 5:1.
 3. The radiation-imageable element of claim 1,wherein said pores have an average pore diameter from about 10 to about100 nm.
 4. The radiation-imageable element of claim 1, wherein saidaverage pore diameter is from about 10 to about 75 nm.
 5. Theradiation-imageable element of claim 1, wherein said polymer particleshave an average particle diameter from about 1 to about 250 nm.
 6. Theradiation-imageable element of claim 1, wherein said polymer particleshave an average particle diameter from about 10 to about 200 nm.
 7. Theradiation-imageable element of claim 1, wherein said polymer particlescomprise a thermoplastic or thermoset polymer.
 8. Theradiation-imageable element of claim 1, wherein said image-forming layerfurther comprises a pigment.
 9. The radiation-imageable element of claim1, wherein said polymer particles comprise a graft polymer having ahydrophobic polymer backbone and a plurality of pendant groupsrepresented by the formula: -Q-W-Y wherein Q is a difunctionalconnecting group; W is selected from the group consisting of: ahydrophilic segment and a hydrophobic segment; Y is selected from thegroup consisting of: a hydrophilic segment and a hydrophobic segment;with the proviso that when W is a hydrophilic segment, Y is selectedfrom the group consisting of: a hydrophilic segment and a hydrophobicsegment, with the further proviso that when W is hydrophobic, Y is ahydrophilic segment.
 10. The radiation-imageable element of claim 1,wherein said polymer particles comprise a homopolymer or a copolymerformed from polymerization of one or more monomers selected from thegroup consisting of: acrylic acid, methacrylic acid, acrylamide,methacrylamide, ester of acrylic acid, ester of methacrylic acid,hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide,methacrylamide, N-hydroxyethyl acrylamide, N-hydroxyethylmethacrylamide, styrene, p-hydroxystyrene, α-methylstyrene,p-methylstyrene, vinyl acetate, methyl vinyl ether, ethyl vinyl ether,hydroxyethyl vinyl ether, vinylphosphonic acid, vinyl chloride,vinylidene chloride, acrylonitrile, N-vinyl pyrrolidone and N-vinylcarbazole.
 11. The radiation-imageable element of claim 1, wherein saidpolymer particles comprise latex particles, phenol-formaldehyde resin, acresol-formaldehyde resin, melamine-formaldehyde resin, a polyurethaneresin and a combination thereof.
 12. The radiation-imageable element ofclaim 1, wherein said polymer particles have a coagulation temperatureof at least 40° C.
 13. The radiation-imageable element of claim 12,wherein said coagulation temperature is at least 60° C.
 14. Theradiation-imageable element of claim 1, further comprising aphotoconverter.
 15. The radiation-imageable element of claim 14, whereinsaid photoconverter is a dye or pigment.
 16. The radiation-imageableelement of claim 14, wherein said photoconverter is selected from thegroup consisting of: an infrared absorbing dye, carbon black, a metalboride, a metal carbide, a metal nitride, a metal carbonitride,bronze-structured oxide and a conductive polymer particle.
 17. Theradiation-imageable element of claim 1, wherein said hydrophilicanodized aluminum base is an oxide base which comprises oxides and oneor both of phosphates and sulfates of aluminum.
 18. Theradiation-imageable element of claim 17, wherein said oxide base ispresent in a coverage of greater than 100 milligrams per square meter ofsaid hydrophilic anodized aluminum base.
 19. The radiation-imageableelement of claim 18, wherein said oxide base is present in a coverage ofgreater than 500 milligrams per square meter of said hydrophilicanodized aluminum base.
 20. The radiation-imageable element of claim 1,further comprising an overlying layer.
 21. The radiation-imageableelement of claim 1, wherein the ratio of said average pore diameter tosaid avenge particle diameter is from about 0.95:1 to about 2.5:1. 22.The radiation-imageable element of claim 1, wherein said average porediameter is from about 10 to about 40 nm.
 23. The radiation-imageableelement of claim 1, wherein said polymer particles have an averageparticle diameter from about 15 to about 60 nm.
 24. Theradiation-imageable element of claim 1, and further comprising aninterlayer.
 25. The radiation-imageable element of claim 24, wherein theinterlayer comprises silicate, polyvinyl phosphoric acid, or polyacrylicacid.
 26. A radiation-imageable element for lithographic printingcomprising: a hydrophilic anodized aluminum base having a surfacecomprising pores having an average pore diameter from about 10 to about100 nm; and coated thereon an image-forming layer comprising polymerparticles having an average particle diameter from about 1 to about 250nm; the ratio of said average pore diameter to said average particlediameter being from about 0.5:1 to about 5:1.
 27. Theradiation-imageable element of claim 26, wherein said average porediameter is from about 10 to about 75 nm.
 28. The radiation-imageableelement of claim 26, wherein said polymer particles have an averageparticle diameter from about 10 to about 200 nm.
 29. Theradiation-imageable element of claim 26, wherein said polymer particlescomprise a thermoplastic or thermoset polymer.
 30. Theradiation-imageable element of claim 26, wherein said image-forminglayer further comprises a pigment.
 31. The radiation-imageable elementof claim 26, wherein said polymer particles comprise a graft polymerhaving a hydrophobic polymer backbone and a plurality of pendant groupsrepresented by the formula: -Q-W-Y wherein Q is a difunctionalconnecting group; W is selected from the group consisting of: ahydrophilic segment and a hydrophobic segment; Y is selected from thegroup consisting of: a hydrophilic segment and a hydrophobic segment;with the proviso that when W is a hydrophilic segment, Y is selectedfrom the group consisting of: a hydrophilic segment and a hydrophobicsegment, with the further proviso that when W is hydrophobic, Y is ahydrophilic segment.
 32. The radiation-imageable element of claim 26,wherein said polymer particles comprise a homopolymer or a copolymerformed from polymerization of one or more monomers selected from thegroup consisting of: acrylic acid, methacrylic acid, acrylamide,methacrylamide, ester of acrylic acid, ester of methacrylic acid,hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide,methacrylamide, N-hydroxyethyl acrylamide, N-hydroxyethylmethacrylamide, styrene, p-hydroxystyrene, α-methylstyrene,p-methylstyrene, vinyl acetate, methyl vinyl ether, ethyl vinyl ether,hydroxyethyl vinyl ether, vinylphosphonic acid, vinyl chloride,vinylidene chloride, acrylonitrile, N-vinyl pyrrolidone and N-vinylcarbazole.
 33. The radiation-imageable element of claim 26, wherein saidpolymer particles comprise latex particles, phenol-formaldehyde resin, acresol-formaldehyde resin, melamine-formaldehyde resin, a polyurethaneresin and a combination thereof.
 34. The radiation-imageable element ofclaim 26, wherein the ratio of said average pore diameter to saidaverage particle diameter being from about 0.95:1 to about 2.5:1. 35.The radiation-imageable element of claim 26, wherein said average porediameter is from about 10 to about 40 nm.
 36. The radiation-imageableelement of claim 26, wherein said polymer particles have an averageparticle diameter from about 15 to about 60 nm.
 37. Theradiation-imageable element of claim 26, and further comprising aninterlayer.
 38. The radiation-imageable element of claim 37, wherein theinterlayer comprises silicate, polyvinyl phosphonic acid, or polyacrylicacid.
 39. The radiation-imageable element of claim 26, wherein saidhydrophilic anodized aluminum base is an oxide base which comprisesoxides and one or both of phosphates and sulfates of aluminum.
 40. Theradiation-imageable element of claim 39 wherein said oxide base ispresent in a coverage of greater than 100 milligrams per square meter ofsaid hydrophilic anodized aluminum base.
 41. The radiation-imageableelement of claim 39, wherein said oxide base is present in a coverage ofgreater than 500 milligrams per square meter of said hydrophilicanodized aluminum base.
 42. A method of producing an imaged element forlithographic printing comprising the steps of: providing a hydrophilicanodized aluminum base having a surface comprising pores characterizedby an average pore diameter; coating thereon an image-forming layercomprising polymer particles characterized by an average particlediameter, the ratio of said average pore diameter to said averageparticle diameter being from 0.4:1 to 10:1; and imagewise exposing saidimage-forming layer to radiation to produce exposed and unexposedregions.
 43. The method of claim 42, wherein said radiation is thermalradiation.
 44. The method of claim 43, wherein said step of exposingsaid image-forming layer to thermal radiation is carried out using aninfrared laser.
 45. The method of claim 42, further comprisingpostbaking said imaged element.
 46. An imaged element prepared by themethod of claim
 42. 47. The method of claim 42, wherein the step ofproviding the anodized aluminum base comprises anodizing an aluminumbase in phosphoric acid.
 48. The method of claim 42, wherein the step ofproviding the anodized aluminum base comprises anodizing an aluminumbase in sulfuric acid.
 49. The method of claim 42, wherein the step ofproviding the anodized aluminum base comprises etching the anodizedaluminum base to increase the average pore diameter.
 50. The method ofclaim 42, and further including the step of forming an interlayer on theanodized aluminum base.
 51. A method of producing an imaged elementhaving complementary ink receiving and ink rejecting regions, saidmethod comprising the steps of: providing a radiation-imageable elementfor lithographic printing comprising: a hydrophilic anodized aluminumbase having a surface comprising pores; and coated thereon, aimage-forming layer comprising polymer particles, the ratio of saidaverage pore diameter to said average particle diameter being from about0.4:1 to about 10:1; imagewise exposing said image-forming layer toradiation to produce exposed and unexposed regions; and contacting saidimagewise exposed image-forming layer and a developer to selectivelyremove said exposed or said unexposed regions.
 52. The method of claim51, wherein said contacting selectively removes said unexposed regions.53. An imaged element prepared by the method of claim 51.